Method and apparatus for controlling gravity liquid flow, and for continuous metal billet casting



H. JONES Mach 4, 1958 2,825,?Q4

METHOD AND APPARATUS FOR CONTROLLING GRAVITY LIQUID mow, AND FORcommuous METAL BILLET CASTING 2 Sheets-Shet l Filod March 16. 1954INVENTOR.

March 4, 1958- s. H. JONES 2,825,104

METHOD' AND APPARATUS FOR CONTROLLING GRAVITY LIQUID FLOW, AND FORCONTINUOUS- METAL BILLET CASTING Fill d March 16, 1954 2 Sheets-Sheet 2I I I INVENTOR.

United States Patent METHOD AND APPARATUS FOR CONTROLLING GRAVITY LIQUIDFLOW, AND FOR CONTINU- OUS METAL BILLET CASTING Sam H. Jones, Flossmoor,Ill., assignor to Askania Regulator Company, Chicago, 111., acorporation of Illinois Application March 16, 1954, Serial No. 416,461

18 Claims. (Cl. 2257.2)

In its broadcast application the present invention relates to regulationof the volume rate of gravity flow of a liquid material, from an upper,supply body of liquid contained in a first and higher receptacle,through an orifice that is located below the surface of that body ofliquid material, and to a receiving body thereof contained in a lowerreceptacle disposed to receive the liquid discharged through theorifice.

A typical field of utility of the invention is in a situation whereinthe material is continuously withdrawn from the lower receptacle, at avolume rate which may vary, in which case the invention may be used tomaintain the volume rate of fluid discharge through the orificesubstantially equal to the rate of withdrawal, and/ or a situationwherein the supply body of liquid material in the upper receptacle isperiodically replenished by added batches, whereby the liquid at theorifice is subject to periodically varying head pressures. In the lattercase the invention may be either or both used to maintain the volumerate of discharge through the orifice constant under the varying head,and/or again made to substantially equal the volume rate of withdrawalof the material from receiving body contained by the lower receptacle.

A very important field of application of the invention, and which hasbeen selected for purposes of disclosure, is that of continuous metalcasting, for example, the continuous casting of molten metal into anopen top and open bottom mold, wherein the metal continuously movesdownward through the mold, solidifying from molten condition at the topto solid condition at the bottom of the mold, and being continuouslywithdrawn therefrom in the form of solid, elongate billet stock.

While this continuous billet casting is being commercially worked, ithas, prior to the present invention, presented such serious problems asto place it on the border line between practical and impracticaloperation.

Reference is made to United States Patent to Webster, No. 2,246,907,dated June 24, 1941, which enumerates certain of the ditficulties andproblems of continuous billet stock casting. For example, the rate ofwithdrawal of solidified billet stock from the mold bottom may have tobe varied by reason of variation in temperature of the molten metal, itsrate of solidifying, etc. In continuous casting, as generally practicedat the present time, the metal is cast from a supply body that iscontainedv in a pour box, having a relatively low level dischargeorifice, and the supply body is periodically replenished by ladlebatches that are rapidly poured or dumped into the pour box, to bethereafter discharged gradually through the pour orifice to the mold.This periodic replenishment provides periodically varying head of moltenmetal above the pour box discharge orifice, a varying pressure at theorifice, and a variation in volume rate of discharge of the metal. Alsovariation in the gravity rate of flow of the molten metal may be causedby varying viscosity of the molten metal. 1

The present invention atfords a novel means and method of overcomingsuch factors as tend toresult in uncon- "ice trolled variation in rateof discharge by gravity of molten metal through an orifice, and alsopermits that rate to be maintained practically equal to a variablevolume rate of withdrawal of metal from the lower, receiving body ofmetal.

In the accompanying drawings:

Fig. 1 is a somewhat schematic vertical section, showing a continuousbillet casting assembly including one embodiment of the invention.

Fig. 2 is a fragmentary detail section showing a minor modification ofstructural arrangement for practising the invention.

Fig. 3 is a view similar to Fig. 1, showing a more complex embodiment ofthe invention.

Referring to Fig. l, the continuous billet casting apparatus thereinshown includes a stationarily mounted pour box 5, having at its bottom adischarge orifice 6 that overlies a mold 7 that has an open top 8, anopen bottom h, and double walls providing space 10 for circulation of acooling medium. As is the general practice, mold 8 is mounted forvertical vibration through a distance indicated at 11, which in practiceis of the order of threequarters of an inch, and is vibrated by suitablemechanism, not shown. For continuously supplying molten metal to mold 8,pour box 5 periodically has poured into it batches of molten metal,which forms therein a supply body 12 of metal in molten, liquidcondition. ,This periodic replenishment may be accomplished by batchesof molten metal poured into box 5 by a ladle 13, at such intervals as tomaintain continuous discharge of metal through orifice 6 and to the opentop 8 of mold 7. This metal forms in mold 7 a body 14 that is molten atthe top of the mold, that continuously moves downwardly through the moldand solidifies therein, being withdrawn continuously from the bottom ofthe mold as elongate, solid billet stock 15. This billet stock iswithdrawn by a suitable driving mechanism, such as that shown by theabove-identified patent, and including a pair of motor driven gripperwheels, herein designated 16, and, as also set forth in that patent,these wheels may be driven at selectively variable speed to permitadjustment of the travel time of metal through mold 7.

It will be readily apparent that such factors as viscosity of moltenmetal forming the supply body 12, and varying depth of that body whichprovides a varying head at orifice 6 will tend to vary the volume rateof discharge of the liquid, molten metal through that orifice,additionally, that any variance betweeen volume rate of that dischargeand volume rate of withdrawal of metal from the mold, as solid billetstock 15, will result in variation of the level of the top surface 17 ofthe body 14 of metal in the. mold, which may cause overflowing of themold, or insufiicient travel time of the metal within the mold forsolidification, depending on the sense of such variance.

In conformance with the more general aspects of the invention,regulation of the volume rate of flow of metal in molten condition, fromthe supply body llcontained by pour box'S, and by gravity dischargedthrough orifice 6 to the receiving body of molten metal comprisingtheupper portion of the body 14 of metal in mold 7, a chamber or'space 20,containing the discharge side or outlet of orifice 6 and the open top 8of mold '7, and overlying the top surface 17 of the receiving body 14 ofmetal, is enclosed in a gas tight wall structure 21. As shown in Figs. 1and 3, this wall structure, to accommodatevertical vibration of mold 7relative to the stationary pour box 5,

may be of the axially semi-collapsible or other flexible pending fromthe pour box bottom and entered into an 7 3 annular trough 24 carried bythe top of the mold and containing a liquid sealing medium, such asmercury. In either case, a gas tight seal is provided at the top of wallstructure 21, as by joining it with a plate 25 secured to the p'o'u'rbox bottom, and at the bottom, either by sealing the flexible wall 21 tothe top of mold 7, or by the sealing tr'ou'gh arrangement 24 of Fig. 2.

Provision is made for varying the magnitude of pressure of a gaseousmedium filling chamber 20 within wall structure :21, thereby to increaseand decrease rate of discharge of molten metal through orifice6,respectively by decreasing and increasing the pressure of that medium.Additionally, and as shown, such gas pressure variation may beaccomplished automatically, as to maintain voltime rate of metaldischarge constantin spite of periodic head variations caused byperiodic replenishment of the supply body 12, and/or to maintain thevolume rate of molten metal pouring substantially equal to the volumerate of withdrawal of metal from mold 7 in the form of solidified billetstock.

As a means of selectively varying the pressure of the gaseous mediumthat is maintained under pressure in chamber 20, there is shown in Figs.1 and 3 a supply line 28 that communicates with chamber ZO for theretosupplyinga suitable gaseous medium delivered by a source at somesuitable preselected maximum pressure. A suitable system for selectingthe pressure exerted in chamber 20, is one that varies the ratio betweenvolume rate of supply of the gaseous medium to chamber 20 and the volumerate of exhaust of the medium from the chamber. In Figs. 1 and 3, ableed or exhaust line 29 serves to exhaust the gas from the chamber, andeither or both a flow rate regulating valve 30 in supply line 28 and/ora flow rate regulating valve 31 in the exhaust line 29, may be employedto adjust that ratio. Thus valve 30 may be opened and closedrespectively to increase and decrease pressure in chamber 20 byincreasing and decreasing the ratio of volume rate of supply to that ofexhaust, and/or valve 3l may be opened or closed to decrease andincrease pressure in chamber 20, also by decreasing and increasing theratioiof volume rate of supply to that of exhaust.

The automatic control system of Fig. 1, by means of which rate of moltenmetal discharge through orifice 6 may be maintained substantially equalto rate of billet stock withdrawal is shown as including means, closelyresembling those of the above-identified patent, for detecting the levelof the top surface 17 of the receiving body 14 of metal in mold 7, andgenerating asignal of a magnitude corresponding to that level andvarying in proportion to changestherein. Such means may include aphotosensitive cell 35 to which light emitted by the surface 17of themoltenbody of metal in the mold is conducted by a quartz rod 36, in'such fashion that intensity of illumination of cell 35 increases anddecreases with rise and descent of surface 18. The electrical signaloutput of cell 35, increasing and decreasing with intensity ofillumination of cell 35, is imposed on a servomotor system 37, theoutput element 38 of which is connected to the control element of valve30, in such fashion as to open that valve more widely when the level ofsur face 17 rises, thereby increasing the ratio of volume rate of supplyto that of exhaust of the gaseous medium correspondmgly raising thepressure in chamber 20, and decreasing the rate of molten metaldischarge through ori fice 6, by increasing the resistance theretoexerted by the gaseous medium. Opposite operation occurs upon a descentof surface 17. Thus, by suitable circuitry and arrangements ofservomechanism 37, output element 38 and valve 30, the level of surface17 can be made to remain quite constantly at a preselected level duringchanges of rate of billet stock withdrawal, and/or changes of suchfactors. as may afiect the rate of metal discharge through orifice 6, asvariation in head provided by body 12, or viscosity of the molten metal.

In some cases it may be desirable to provide for an auxiliary controleffect, somewhat of the nature of an anticipatory regulating operation,that acts rapidly upon replenishment of the upper, supply body 12 ofmolten metal, to increase the gas pressure in chamber 29, independentlyof the level of surface 18 of the lower, receiving metal body. Fig. 3shows an arrangement for providing such control.

This arrangement comprises means for detecting the magnitude of the headof molten metal that is effective at the entrance or upper side ofdischarge orifice 6, producing a signal of a magnitude that isproportional to that head, and utilizing that signal to vary therelative rates of volume supply and exhaust rates of the gaseous mediumto and from chamber 26, to increase and decrease the ratio of supply toexhaust respectively with increase and decrease of the head of metal inpour box 5. Since the gaseous medium supply. and exhaust rate ratio isalso subjected to control from the lower metal body surface 17, suchcontrol by head or depth of the supply body 12 may not result in actualincrease or decrease of pressure in chamber 21, but may result only in atendency toward such an increase or decrease.

Conveniently, as shown in Fig. 3, the device for measuring the depth ofsupply body 12, or of the head thereby provided, comprises a secondsurface level detector, in cluding a photosensitive cell 40 and a quartztube 41 in an arrangement to vary intensity of illumination of cell 40by light emitted from the top surface 42 of the supply body of moltenmetal in pour box 5, with rise and descent of that surface 42. Thesystem is so arranged that the pressure of the gaseous medium in chamber2t) is proportional to an algebraic summarization of componentsrespectively proportional to the magnitudes of signal outputs of cell40, and a second cell 44 that is arranged to detect the level of the topsurface 17 of the receiving body 14 of metal in mold 7, in anarrangement similar to that of Fig. l. Conveniently, and as shown, suchsummarization may be accomplished at chamber 20 it self, by the verysimple expedient of operating the valve 30 that controls volume rate ofgas supply by a servomechanism 45 that is controlled by the output ofone cell, shown as 44, while the exhaust rate control valve 31 isoperated by a second servomechanism 46 that is controlled by the othercell, here 40.

By such an arrangement, while the pressure in chamber 20, exertedagainst discharge of molten metal through orifice 6, primarily andinherently is under control of cell 44 and changes in the level ofsurface 17, the replenishment of supply body 12 tends to provide a rapidincrease in the ratio of rate of gaseous medium supply to rate ofexhaust, by reduction of the latter rate, thus minimizing the laggingeffect that may occur if the change in rates of gas supply and exhaustare delayed until rise of surface 17 as a result of increased head ofmolten metal above orifice 6.

From the above it will be evident that there are certain basic conceptsof method and apparatus presented by the invention herein disclosed, andthat many variations from the specific embodiments 'above described inan exeinplary way may be resorted to within the limits of the invention,which limits are to be ascertained solely from the appended claims.

I claim:

1. In the continuous gravity casting of molten metal from-anintermittently replenished molten supply body in a pouring box, throughan orifice therein, and to a receiving body of molten metal in an openbottom billet mold wherein said metal continuously solidifies and fromthe bottom of which the solidified metal is continuously withdrawn as anelongate billet, the method of maintaining the volume rate of moltenrnetal flow through said orifice substantially equal to the volume rateof with drawal of solidified metal from said mold, said methodcomprising supplying to and exhausting from a confined space located atthe discharge side of said orifice and overlying said receiving body, agaseous medium under pressure, detecting and developing a first controlsignal from the level of the top surface of said receiving body ofmetal, by said signal varying the relative volume rates of supply andexhaust of said gaseous medium to increase and decrease the ratio ofsupply rate to exhaust rate in respective response to rise and descentof said surface level, detecting and developing a second control signalfrom the level of the top surface of said intermittently replenishedsupply body, and by said second control signal varying the ratio betweensaid volume flow rates of supply and exhaust of said gaseous medium toincrease the ratio of supply rate to exhaust rate in respective responseto rise and descent of said supply body top surface level.

2. In apparatus for continuous casting of molten metal, which includes apour box for containing a supply body of the molten metal and havingtherein an orifice for gravity flow of metal from said body, a moldingdevice comprising a receptacle disposed beneath said orifice forreceiving molten metal, therefrom and means for continuously withdrawingmetal from saidreceptacle; means for detecting the volume rate ofwithdrawal of metal from saidreceptacle and generating a signal of amagnitude proportional thereto, means for maintaining volume rate offiowof molten metal through said orifice substantially equal to said volumerate of metal withdrawal, comprising gas tight structure enclosing aspace surrounding'said orifice and the top of said receptacle, a body ofgas under pressure enclosed by said structure, and means responsive tomagnitude of a signal developed by said detector and signal generatingmeans for increasing and decreasing the pressure of said gasrespectively in response to decrease and increase in said withdrawalrate and in a range of pressure of suificient magnitudes tocorrespondingly vary the rate of metal flow through said orifice.

3. In apparatus for continuous casting of molten metal, which includes apour 'box for containing a supply body of molten metal and havingtherein an orifice for gravity fiow of metal from said body, a moldingdevice comprising a receptacle disposed beneath said orifice forreceiving and containing a body of molten metal therefrom and means forcontinuously withdrawing metal from said receptacle; means for detectingand generating a signal of a magnitude that varies with the level of thetop surface of a body of molten metal in said receptacle, means formaintaining the volume flow rate of molten metal through said orificesubstantially equal to said volume rate of metal withdrawal, comprisinggas tight structure enclosing the discharge side of said orifice and thetop of said receptacle, means for introducing gas underpressure to theinterior of said receptacle, means for exhausting gas therefrom, andmeans responsive to magnitude of a signal developed by said detector andsignal generating lmeansfor varying the relative volume rates of gasflow through said supply and exhaust means to increase and decrease theratio of supply rate to exhaust rate in respective response to rise anddescent of said level, and in va range of magnitudes of pressuresufiicient to correspondingly affect rateof flow of the metal throughsaid orifice.

4. In apparatusfor continuous casting of molten metal, which includes apour box for containing a supply body of moltentmetal and having thereinan orifice for gravity flow of metal from said body, and a moldingdevice comprising a receptacle disposed beneath said orifice forreceiving and containing a body of molten metal therefrom and means forcontinuously withdrawing metal from saidreceptacle; means for detectingthe level of the top surface of a supply body of molten metal containedby said pour box and generating a signal of a magnitude rthat varieswith change of said level, gas tight structure enclosing the dischargeside of said orifice and the top 2,825, tea

of said receptacle, and means operative in response to variation inmagnitude of said signal for increasing and decreasing pressure of agaseous medium contained by said structure in respective response torise and descent of said level, and in a range of magnitudes of pressuresuflicient to correspondingly afiect rate of flow of the metal throughsaid orifice.

5. In apparatus for continuous casting of elongate billet stock, andwhich includes a stationary pour box for containing a supply body ofmolten metal and having an orifice for discharging metal from said body,molding means comprising a vibratory, open bottom mold having a topopening disposed to receive molten metal from said orifice and adaptedto contain a continuously downwardly moving body of metal that is moltenat the top and solid at the bottom of the mold and means for continouslywithdrawing solidified metal as elongate billet stock from the open moldbottom, and means for detecting and generating a signal of a magnitudevarying with the volume rate of solid metal withdrawal from said moldbottom; means for maintaining the volume rate of molten metal dischargethrough said orifice substantially equal to said volume withdrawal rate,comprising gas tight structure having a wall connected with said moldand pour box, enclosing the discharge side of said orifice and said moldtop opening, and arranged to permit vibration of said mold relative tosaid stationary pour box, and means responsive to said signal forincreasing and decreasing the pressure of a gaseous medium enclosed bysaid structure respectively in response to decrease and increase in saidwithdrawal rate, and in a range of magnitudes of pressure sufiicient tocorrespondingly affect rate of tlow of the metal through said orifice.

6 In apparatus for continuous casting of elongate billet stock, andwhich includes a stationary pour box for containing a supply body ofmolten metal and having an orifice for discharging metal from said body,molding means comprising a vibratory, open bottom mold having a topopening disposed to receive molten metal from said orifice and adaptedto contain a continuously downwardly moving body of metal that is moltenat the top and solid at the bottom of the mold and means forcontinuously withdrawing solidified metal as, elongate billet stock fromthe open mold bottom, and means for detecting and generating a signalthe magnitude of which varies with rise and descent of the level of thetop surface of a body of metal contained by said mold; means formaintaining the volume rate of molten metal discharge through saidorifice substantially equal to the volume rate of withdrawal of solidmetal from said mold bottom, comprising gas tight wall structureattached to said pour box and mold, enclosing the discharge side of saidorifice and said open mold top, and arranged to permit vibration of saidmold relative to said pour box, means for supplying to and exhaustingfrom the interior of said wall a gaseous medium under pressure, andmeans responsive to the magnitude of said signal for varying therelative volume rates of supply and exhaust of said gaseous medium toincrease and decrease the ratio of supply rate to exhaust rate inrespective response to rise and descent of said level, and in a range ofmagnitudes of pressure suificient to correspondingly afiect rate of flowof the metal through said orifice.

7. The method of controlling flow rate of liquid through an orifice ofconstant effective cross sectional area, that comprises maintaining aconfined body of a gaseous medium at the delivery side of said orificeunder pressure of sufiicient magnitude to affect rate of liquid fiowthrough said orifice by counter-pressure resistance exerted by saidmedium, and adjusting the pressure of said body inverse-' 1y withrequired changes in said flow rate and independently of changes inpressure of said liquid. 7 a

8. The method of controlling gravity flow rate of liquid through anorifice, that comprises maintaining a conufi pi wbpdy of agaseous mediumat the delivery side of .gsaid orifice under pressure of sufficientmagnitude to affect rate of fiow through said orifice bycounter-pressure resistance exerted by said medium, developingindependently ofithe pressure of said gaseous medium a control signal ofmagnitude proportional to magnitude of variance between said fiow rateand a required fiow rate, and by said ,control signal increasing anddecreasing pressure of said medium respectively as said flow rateexceeds or is less than the required flow rate.

9. The method of controlling gravity fiow rate of material in liquidform through an orifice and to a body from-whieh said material isremoved continuously, said method comprising maintaining an enclosedgaseous medium in a confinedspaceat the discharge side of said orificeand overlying said body of material under pressure of sufiicientmagnitude to affect rate of flow or" the liquid through said orifice bycounter-pressure resistance exerted ,by said medium, detecting anddeveloping a control signal from changes in the level of the top of saidbody of material and independently of the magnitude of pressure of saidmedium, and in response to variation in said control, signal increasingand decreasing the pressure of said gaseous medium respectively, whensaid top level rises and descends and as the sole means of controllingsaid flow rate.

10. The method of controlling gravity fiow ofmaterial in liquid formfrom an upper body the depth of which is variable, through an orificespaced below the surface level of said body and providing a flow path ofconstant effective cross sectional area, whereby a variable head existsabove said orifice, and to a second body of said material below saidorifice and from which said material is withdrawn continuously, saidmethod comprising, maintaining a confined body of a gaseous medium atthe discharge side of said orifice and overlying the surface of the saidlower, body under pressure of a magnitude sufiicient to affect rate offlow of the liquid through said orifice by counterpressure resistanceexerted by said medium, detecting and developing a control signal'fromchanges in the level of the upper surface of at least one of said bodiesand independently of magnitude of pressure of said medium, and by saidcontrol signal increasing and decreasing the pressure of said gaseousmedium respectively in response to rise and descent of a surface level,so detected as the sole control of said flow rate.

11. The method of controlling gravity flow of liquid from a body ofvarying depth, and through an orifice spaced below the surface of saidbody, whereby a variable head is provided, said method comprising,maintaining a confined body of gaseous medium at the discharge side ofsaid orifice under pressure within a range of magnitudes sufficient toaffect rate of how of the liquid through said orifice, detecting anddeveloping a control signal from variations in the level of the surfaceof said body ofliquid, and increasing and decreasing the pressureof saidgaseous medium respectively in response to variations in said controlsignal responsive respectively to rise and descent of ,said level.

12. The method of controlling flow rate of liquid through an orificethat comprises maintaining constant the etfective cross sectional areaof the How path provided by said orifice, supplying to and exhaustingfrom a confined space at the discharge side of the orifice a gaseousmedium under pressure of magnitude sufiicient to affect flowrate of theliquid through said orifice by counter-pressure resistance exerted bysaid medium, and as the sole control of said fiow rate varying therelative volume flow rates of supply and exhaust of said medium to varythe pressure thereby exerted in said spaceand that opposes flow ofliquid through said orifice, inversely with required changes in rate offlow of said liquid through said ,orifice.

13.The method of controlling gravity fiow rate of liquid .from .anupper, supply body of varying depth, throughan orifice spaced below thesurfaceof said body, wherebya variable head is provided, and to a lower,receiving body from which said material tisldrawn continuously, saidmethod comprising continuously supplying to and exhausting from aconfined space enclosing the delivery side of said orifice and the uppersurface of said lower body a gaseous medium under pressure of magnitudesutficient to affect rate of flow of the liquid through said orifice,detecting and developing from the level of the top surface of the saidreceiving body and independently of the magnitude of pressure of saidmedium a first control signal and by said signal varying the relativevolume flow rates of supply and exhaust of said gaseous medium toincrease and decrease the ratio of supply rate to exhaust rate inrespective response to rise and descent of said level, detecting anddeveloping second control signal from the level of the top surface ofsaid upper supply body, and by said second control signal varying therelative volume flow rate of supply and exhaust of said gaseous mediumto increase and decrease the ratio of supply rate to exhaust rate inrespective response to rise and descent of said uppeiysupply body topsurface level.

14. In the continuous gravity casting of molten metal from a moltensupply body in a pouring box, through an orifice therein and to areceiving body of molten metal in a molding device wherein said metalsolidifies and from which solidified metal is continuously withdrawn,the method of maintaining volume fiow rate of molten metal through saidorifice substantially equal to the volume rate of withdrawal ofsolidified metal from said molding device, said method comprisingsupplying to and exhausting from a confined space located at thedischarge ,sideof said orifice and enclosing the top surface of saidreceiving body of molten metal, a gaseous medium under pressure of amagnitude sufiicient to affect rate of flow of the metal throughsaidorifice, developing independently of the magnitude of pressure ofsaid gaseous medium a controlsignal having a magnitude proportional tothe volume rate of withdrawal of solidified metal from said moldingdevice, and by said control signal varying the relative volume rates ofsupply and exhaust of said gaseous medium to increase and decrease theratio of supply rate to exhaust rate of said gaseous medium inrespective response to decrease and increase in said volume rate ofwithdrawal.

15. In the continuous gravity casting of molten metal from a moltensupplybody in a pouring box, through an orifice therein and to areceiving body of molten metal in an open bottom billet mold whereinsaid metal continuously solidifies and from the bottom of which thesolidified metal is continuously withdrawn as an elongate billet, themethod of maintaining the volume rate of molten metal flow through saidorifice substantially equal to the volume rate of withdrawal ofsolidified metal from said mold, said method comprising supplying andexhausting a gaseous medium to and from a confined space located at thedischarge side of said orifice and above said receiving body of metal inthe mold and at respective rates to maintain said medium within saidspace at a pressure of suflicient magnitude to affect rate of flow ofthe metal through said orifice, detecting and developing from the levelof the top surface of at least one of said bodies and independently ofthe magnitude of pressure of said gaseous medium a control signaL'and indirect response to said control signal varying the relative volume ratesof supply and exhaust of said gaseous medium to increase and decreasethe ratio of supply rate to exhaust rate in respective response to riseand descent of a said top surface level so detected.

16. In the continuous gravity casting of molten metal from anintermittently replenished moltensupply body in a pouring box, through'an orifice therein, and 1013 receiving body of molten metal in an openbottom billet mold wherein said metal continuously solidifies and fromthe bottom of which thesolidified metal is continuously withdrawn as anelongate billet, the method of maintaining the volume rate of moltenmetal flow through said orifice substantially equal to the volume rateof withdrawal of solidified metal from said mold, said method comprisingsupplying and exhausting a gaseous medium to and from a confined spacelocated at the discharge side of said orifice and overlying saidreceiving molten metal body at respective rates effective to maintainpressure of said medium in said space at a magnitude Suicient to afiectrate of flow of the metal through said orifice by counter-pressureresistance exerted by said medium, detecting and developing from thelevel of the top surface of the latter said body and independently ofmagnitude of the pressure of said medium a control signal, and by saidcontrol signal and as the sole means of controlling said flow ratevarying the relative volume flow rates of supply and exhaust of saidgaseous medium to increase and decrease the ratio of supply rate toexhaust rate in respective response to rise and descent of said surfacelevel.

17. In the continuous gravity casting of molten metal from anintermittently replenished molten supply body in a pouring box, throughan orifice therein, and to a receiving body of molten metal in an openbottom billet mold wherein said metal continuously solidifies and fromthe bottom of which the solidified metal is continuously Withdrawn as anelongate billet, the method of maintaining the volume rate of moltenmetal flow through said orifice substantially equal to the volume rateof Withdrawal of solidified metal from said mold, said method comprisingsupplying and exhausting a gaseous medium to and from a confined spacelocated at the discharge side of said orifice and overlying saidreceiving body respectively at rates maintaining said medium within saidspace under pressure of a magnitude to affect rate of flow of the metalthrough said orifice, detecting and developing a control signal solelyfrom the'level of the top surface of said intermittently replenishedsupply body of molten metal and independently of the pressure of saidgaseous medium, and by said control signal varying the relative volumerates of supply and exhaust of said gaseous medium, to increase anddecrease the ratio of supply rate to exhaust rate in respective responseto rise and descent of said top surface level.

18. In apparatus for continuous casting of molten metal, which includesa pour box for containing a supply body of the molten metal and havingtherein an orifice for gravity flow of metal from said body, and amolding device having a receptacle disposed below said orifice forreceiving metal discharged therefrom; means for regulating the volumerate of discharge of molten metal through said orifice comprising gastight structure enclosing the discharge side of said orifice and the topof said receptacle, means for maintaining within said structure agaseous medium under pressure within a range of suflicient pressuremagnitudes to affect the rate of discharge of metal through said orificeby counter-pressure resistance exerted by said medium, and control meansfor adjusting the pressure of said gaseous medium within said range.

References Cited in the file of this patent UNITED STATES PATENTS1,139,888 Mellen May 18, 1915 2,140,607 Thompson Dec. 20, 1938 2,246,907Webster June 24, 1941 2,354,400 Percy July 25, 1944 2,371,604 BrennanMar. 20, 1945 2,457,083 Jordan Dec. 21, 1948 2,544,837 Jordan Mar. 13,1951 FOREIGN PATENTS 891,444 Germany Sept. 28, 1953

